Image sensing apparatuses such as an electronic camera which uses a memory card having a solid-state memory element as a recording medium, and records, plays back, and/or communicates still and moving images are commercially available.
Some of the electronic cameras comprise a plurality of photographing recording modes such as a photographing recording mode (to be referred to as a “JPEG mode” hereinafter) for an image signal form (e.g., JPEG format) that is irrespective of the pixel array of image sensing devices such as CCDs or CMOSs and complies with a predetermined compression method or the like, and a photographing recording mode (to be referred to as a “CCD-RAW mode” hereinafter) for an image signal form (e.g., RAW format) corresponding to the pixel array of image sensing devices. The JPEG mode is selected to reduce the data amount of image data to be recorded and put importance on the versatility of the image signal form. The CCD-RAW mode is selected to put importance on the image quality of image data. In this manner, the photographing recording mode can be arbitrarily switched to perform photographing.
Image data photographed in the JPEG mode undergoes predetermined color conversion, color correction, tone correction, and white balance correction by the developing processing section of the electronic camera. After that, the image data is converted into a JPEG image signal form and recorded on a memory card or the like. To the contrary, image data photographed in the CCD-RAW mode is converted into a predetermined RAW image data format without changing an image signal form corresponding to the pixel array of image sensing devices, and is recorded on a memory card or the like.
Image data in the RAW image data format (to be referred to as “RAW data” hereinafter) can undergo predetermined color conversion, color correction, tone correction, and white balance correction by a developing processing program executed by a personal computer or the like or by developing processing performed by developing hardware such as an image reproduction device. The processed RAW data can be displayed and checked on a display device. The developing program and developing hardware can perform image quality settings such as white balance correction, contrast correction, sharpness, and color density adjustment which meet user's tastes, while maintaining the quality of image data without any degradation. The features of digital image data which allows processing an image can be exploited without degrading the image quality.
Compared to analog information, digital information can be easily processed without degrading the quality. In other words digital information is readily processed. To prevent copying, tampering, and illicit use of digital information, there is proposed a technique of embedding digital watermark information in an image.
Digital watermark information is embedded such that even if the digital watermark-embedded digital information is normally reproduced, the digital watermark is not recognized by the human eye. As a typical information embedding method using a digital watermark, a photographed image undergoes frequency conversion such as high-speed Fourier transform, discrete cosine transform, or wavelet transform, information is attached to the frequency domain, and inverse transform is executed to embed the information as digital watermark information. Typical examples of embedded information are copyright information and user information.
Embedding of digital watermark information is considered to be effective for preventing copying, tampering, and illicit use of a digital image photographed by the electronic camera.
Image data photographed in the JPEG mode undergoes predetermined developing processing and JPEG compression processing in the electronic camera. The image data further undergoes digital watermark information embedding processing and is recorded on a memory card. Prevention of copying, tampering, and illicit use of the photographed digital image can be guaranteed at the photographing time point.
When, however, digital watermark information is embedded in image data photographed in the CCD-RAW mode and the image data is recorded on a memory card, the embedded digital watermark information is greatly damaged in developing processing by the developing processing hardware or developing hardware. Prevention of copying, tampering, and illicit use of the digital image photographed in the CCD-RAW mode cannot be guaranteed at the photographing time point.